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Tube Amp for Martin Logan Speakers

Hi, I love tube sound through my Martin Logan Aerius-i fronts and Cinema-i center. I currently have a Butler 5150 which is a hybrid, but it busted on me and would cost $700 to fix. I've had china stereo tube amps that were pretty good and gave true tube sound, but not enough drive for higher volumes. I live in condo, so not like I can blast music anyways but still. I got the Butler because I wanted 5 channel tube sound for home theatre (The piercing sound from my Denon 3801 receiver was not pleasant to my ears). It appears there are only three multi-channel tube amps around, from Mcintosh, Butler 5150, and Dared DV-6C. The latter two are hybrids, and the last one was one of the worst tube amps i've ever heard. I have no clue why 6Moons gave the Dared a 2010 award, but maybe it's because it produces only 65W.

So since multichannel tube amps are hard to come by, and they tend to be hybrid, I was thinking maybe it would be best to get three true tube monoblocks to power my fronts. Thing is I wonder if they will be underpowered for my speakers, and not sure which ones are decent for the price. Maybe China made ones would suffice, and they still go for pretty expensive price. I'm wondering if anybody knows of a decent powerful tube monoblock that is affordable, because I can't pay $3000 per block. or maybe best to just repair my Butler. Thing is, I'm not confident that it is reliable. The tubes are soldered in which is weird, and i've taken it to a couple repair guys who both said that the design is not good, because it's very tight inside and more susceptible to being fried from DC voltage areas. it's too sensitive.

Any suggestions for tube monoblocks, even if china made ones? the holy grail for me would be Mcintosh tube amp, but they are hard to come by. Thanks.

smurfmand70
jandidden
8 posts
 
Atmasphere, your conclusion that someone (certainly not me!) would think if you lower the Zout to zero in a preamp, it can effortlessly drive 4 ohms, is rather far-fetched. As I'm sure you know, Zout has NOTHING to do with what you can or cannot drive, and I would expect that most people here would be well aware of that. A D-type battery cell has a Zout of less than an ohm but nobody would expect it to be able to start their car. :-) . I really have no idea what gave you that particular idea.

BTW I gave the example of ss amps' Zout being caused by for instance the transistor gain droop with increased load current. In a tube amp, there are causes for 'Zout' like the internal output tube(s) resistance and transformer losses that cause a drop in output voltage if you increase load current (for instance by connecting a lower impedance speaker). My point was that this Zout in the amp is largely 'virtual' in the sense that you cannot point to a resistor in the amp that would be the Zout. Now what nfb does is making the drop in output voltage with more load less so, thus causing the Zout to appear lower.

Actually it is quite easy to measure Zout on your amp. Just connect an 8 ohms resistor as load and set Vout to say 8 volts. The Iload is therefore 0.5 amps. Now connect a 4 ohms resistor and let's say the Vout drops to 7 volts. The Iload is now of course 7 V/4 ohms = 1.75 amps. So we now know that Vout drops 1 V if the current increases 0.75 amps. Therefore Zout is 1 V / 0.75 amps = 1.3334 ohms. Easy, no?
jandidden
8 posts
 
Atmasphere, I read your last post again - are you trying to say that even when nfb decreases the voltage drop due to increased current output (the Zout), that doesn't mean that the amp can all of a sudden deliver more power? If so, I fully agree. The amp has it's intrinsic limits in output current and output voltage and nfb cannot change that.
Even with nfb, when the output voltage goes up, it eventually gets up to the supply voltage and cannot go higher of course. Same with the output current - the current capability of the amp cannot increase due to nfb. What nfb will do is to keep 'trying' (if you will excuse this antropomorphism) to keep up the output voltage right up to the supply voltage. This is, of course, the reason why an nfb amp generally clips much sharper than a non-nfb amp.
atmasphere's avatar
atmasphere
11,807 posts
 
^^ Ah- good.

And we now also see why the Power Paradigm is still around some 60 years after it was supposed to be supplanted by the Voltage Paradigm: and that is because amplifiers operating under the Power Paradigm tend to make less odd ordered harmonic distortion.

This is partially because nfb will add trace amounts of odd ordered harmonics, even when used in large amounts.

The human ear/brain system is very sensitive to these distortions, more so than anything else, as it uses higher ordered harmonics to determine how loud a sound is. As a result, nfb will make an amplifier sound brighter than it really should be (regardless of tube or transistor) because the ear/brain system translates distortion as tonality.

This is why two amps on the bench might have the same bandwidth but one can sound bright and the other doesn't.
jandidden
8 posts
 
My 2nd post above, where I say: 'The Iload is therefore 0.5 amps' should be of course 1 amp (from 8 V across 8 ohms). Duhhh. :-)
unsound
7,329 posts
 
"...IOW the ML ESLs are a low impedance Power Paradigm loudspeaker..."
Perhaps I'm missing something here, but do these graphs seem to suggest something else?
http://www.stereophile.com/reference/810/index.html
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